Bi-N-TiO2 nanoparticles were synthesized via anneal after a simple sol-gel combined hydrothermal method. X-ray diffraction (XRD), UV-Visible diffuse reflectance spectra, Scanning Electron Microscope (SEM) and X-ray photoelectron spectra (XPS) confirm that the grain sizes are almost uniform diameters of about 11 nm, the response to light extends to visible region, the doped ions substitute some of the lattice titanium atoms, and furthermore Bi3+ and Bi4+ ions coexist. The photodegradation of acid orange 7 (AO7) is used to evaluate the photocatalytic activity of the prepared Bi-N-TiO2 nanoparticles. The experiments indicated that Bi-N-TiO2 showed higher photocatalytic activity than that of P25, TiO2, N-TiO2 and Bi-TiO2 in the visible light area and ultraviolet light. The improvement of photocatalytic activity of Bi-N-TiO2 is more likely because the N doping causes the visible light response and improves the quantum yield and photocatalytic activity of TiO2, and Bi doping causes the enhancement of the separation of photogenerated charges.